Cannot Resolve 502 Error

Question

We consistently get this error after using the web app for short periods of time:

I have been through this document, but have not found a solution yet. There is a public IP address in front of the web app. I think that this is a gateway and they gateway is not getting a response from the back-end API, but I don't have any logs at the IP address level to know whether this is true or not. I have mostly been focusing on the Application Insights logs. I don't see any exceptions or other information that tells me that the back-end is having any issues. The app mostly works OK, and then stops responding. The app doesn't seem to have any issues when I run it locally.

This is the memory working set metric for the web app. It does seem to rise until it drops right off, but I can't find any correlation with the 502s at this time.

CPU time, again with some strange spikes.

In the gateway logs, I see lots of httpStatus_d = 502 messages, but they don't really tell me anything. They don't tell me what Url in the back-end the browser was trying to hit, so I can't diagnose the issue.

Edit: actually I was wrong. ^^ the request Url is in the requestUri_s column in the logs. This looks like it might help a lot.